Bug 1539796 - Ccov build: fatal error: 'mozilla/Sandbox.h' file not found r=Alex_Gaynor

Add missing MOZ_SANDBOX preprocessor check before including Sandbox.h to fix the code coverage build.

Remove unused nsMacUtilsImpl.h #include.

Differential Revision: https://phabricator.services.mozilla.com/D25287

--HG--
extra : moz-landing-system : lando

dom/media/ipc/RDDProcessHost.cpp

@@ -11,9 +11,8 @@
 
 #include "RDDChild.h"
 
-#if defined(XP_MACOSX)
+#if defined(XP_MACOSX) && defined(MOZ_SANDBOX)
 #  include "mozilla/Sandbox.h"
-#  include "nsMacUtilsImpl.h"
 #endif
 
 namespace mozilla {